As generally known, driving a multiple-winding AC rotating machine having a plurality of multi-phase winding sets by a plurality of inverters can increase the output power or decrease the size of a control apparatus of the AC rotating machine.
One method of current control for a multiple-winding AC rotating machine having a plurality of multi-phase winding sets is to use a separate inverter for each set of windings for current control. However, this method has a problem that magnetic coupling between the windings of each set causes interference between the output currents of the inverters, which causes ripple in the output currents particularly when the gain of a current control system is high, preventing highly responsive control.
In order to solve this problem, for example, a control apparatus for AC rotating machine described in JP-A-03-253293 (PTL 1) is configured to, while variable speed driving an AC rotating machine using a plurality of power converters, detect output currents of the power converters, calculate a sum and difference of the output currents based on the detected values and feedback the sum and difference to current adjusters of the power converters with different control gains to control the output currents of the power converters to be proportional to the command values.
Causing the control gain for the added value (average value) of the output currents of the inverters controlled by the current adjusters configured as above and provided for the respective inverters to be different from the control gain for the unbalanced gain allows the current control responsiveness for the average value of the output currents and the current control responsiveness for the unbalanced value to be separately designed in any appropriate manner. Accordingly, even when the current control of the added value (average value) of the output currents of the inverters is designed to be highly responsive in accordance with a response specification of motor torque control, the current control responsiveness of the unbalanced value of the output currents of the inverters can be always maintained to be an appropriate value, which prevents the control instability due to interference caused by magnetic coupling between the windings of each set, preventing ripple in the output currents from occurring.
However, for performing current control of a multiple-winding AC rotating machine having a plurality of multi-phase winding sets, this configuration requires the same number of coordinate transformation means and command coordinate transformation means including rotating coordinate calculation as the number of the inverters. Generally, rotating coordinate calculation intensively uses trigonometric function and the like, which causes a problem of putting a high computational load on a microcomputer.
In order to solve this problem, for example, a control apparatus for AC rotating machine described in JP-A-2011-152027 (PTL 2) includes: a DC power supply; a plurality of inverters for converting power from the DC power supply into AC power to supply to a three-phase AC rotating machine; a phase current detection means for detecting output current of the plurality of inverters; a three-phase to two-phase conversion means for converting the detected phase current values of the phases detected by the phase current detection means into d-axis and q-axis currents; a current control calculation for generating a representative two-phase voltage command value based on the detected value of the d-axis and q-axis currents converted by the three-phase to two-phase conversion means and d-axis and q-axis current command values; and a two-phase to three-phase conversion means for generating a three-phase voltage command value from the output of the current control calculation; in which both the number of the three-phase to two-phase conversion means and the number of the two-phase to three-phase conversion means are configured to be less than the number of the inverters.
Furthermore, for example, JP-A-2011-15587 (PTL 3) discloses that a multiple-winding AC rotating machine having a multi-phase winding set in which the phase difference between current in a first winding and current in a second winding is 360/(3×M) degrees (“3×M” refers to the number of salient magnetic poles) is to be controlled, allowing the counter-electromotive force and current phase generated by the first winding to be in phase and also allowing the counter-electromotive force and current phase generated by the second winding to be in phase, which allows the motor to be efficiently driven.
A control apparatus for the AC rotating machine disclosed in the PTL 3 includes: a control means for generating a motor drive command in response to an input command; a PWM inverter circuit for supplying drive voltage to the motor in response to the motor drive command; a master motor control unit having a data communication means for providing a motor drive command to another motor control unit; a slave motor control unit having a data communication means for receiving a motor drive command from the master motor control unit and a PWM inverter circuit for supplying drive voltage to the motor in response to the motor drive command from the master motor control unit; 3×M salient magnetic poles (M is an integer more than one); and the motor in which three-phase master windings and slave windings wound around the salient magnetic poles are configured independently of one another. The master windings of the motor are connected to the master motor control unit, while the slave windings are connected to the slave motor control unit. The master motor control unit has a command distributor that provides motor current fed to the slave windings with a phase difference with respect to motor current fed to the master windings and is configured to drive one motor in response to the motor drive command. The command distributor provides a phase difference of 360/(3×M) degrees between the motor current fed to the master windings and the motor current fed to the slave windings.